1. Field of the Invention
This invention relates to storage tanks having liners, especially storage tanks with plastic liners used for storing compressed gaseous fuels. In particular, the present invention is related to a closure assembly for a pressure vessel, which is also a term used to describe such storage tanks.
2. Description of the Prior Art
Pressure vessels are widely used to store liquids and gases under pressure. One growing application of pressure vessels is their use in the storage of alternative fuels, such as natural gas, hydrogen or propane, for use in vehicles such as automobiles. Natural gas and propane are increasingly viewed as preferable to gasoline for fueling vehicles. Accordingly, approaches have been devised for converting gasoline-fueled vehicles to natural gas-fueled or propane-fueled vehicles by retrofitting them to use natural gas or propane instead of gasoline. Additionally, new vehicles are currently being built which are designed to operate using natural gas or propane as the fuel source.
Vessels used for storing natural gases and propane preferably are equipped with a plastic liner, which serves to keep the stored gas from leaking. For a conventional pressure vessel, the liner is overwrapped with composite fibers and epoxy resin to form an outer shell of the pressure vessel. The plastic liner preferably covers the entire interior surface of the pressure vessel, including the neck portion, which defines an access opening for loading fuel. To prevent leakage of fuel at the access opening, a metallic polar boss is roto-molded or injection molded with the liner, and an adapter is installed into the polar boss to finish sealing the liner, and to allow for other metallic parts to attach to the pressure vessel.
The polar boss assemblies for such conventional pressure vessels are therefore provided with two machined parts (i.e., the adapter and the polar boss). This can be disadvantageous as the seal surface of the liner has tight tolerances, and several steps are required to complete the assembly. In addition, in certain of these conventional pressure vessels, additional parts, such as an O-ring or other sealing means, may also be required, thereby further complicating the construction and sealing abilities.